The Paleo Diet (aka The Caveman Diet) is an ancestral way of eating, meaning the way people ate before the agricultural revolution. In other words, if you can catch it, pick it, kill it, or grow it... you can eat it. I'm going to give you the basics, but I strongly recommend you read "The Paleo Solution" and "The Paleo Diet" to truly understand the whos, whats, wheres, whens, and whys of the regimen.
What we should eat:
Meat, Seafood, Poultry
Oils and Fats like olive oil, virgin coconut oil, animal fats (lard, tallow, bacon fat, etc.)
Fruits and Veggies
Nuts and Seeds
Herbs and Spices... people always ask about these two for some reason
What we should NOT eat:
Grains (even whole grains) Remember: Corn is a grain!
Legumes (beans, lentils and peanuts)
Sugar and Artificial Sweeteners
Again if it can be caught, killed or picked, you can eat it.
First things first: Meat and the protein and fat it contains is good for you... we NEED it. Besides, what are our incisors, canines, and molars for? We need the fat because it is necessary for brain function, along with the rest of our body's overall health as well. Nuts and seeds are a good source of fat as well, plus they are delish!
The necessity of fruits and veggies seems like a no-brainer to me. It is a good idea to keep in mind that starchy veggies like potatoes should be consumed in moderation or only on rare occasions, especially if you are overweight or have any ailments.
If food has to be processed before we can eat it, it probably isnt meant for consumption. Grains, dairy, legumes and sugar gives us:
Extreme fluctuation in insulin levels
...just to name a few. Grains and sugars are particularly addictive.
These are a few fun facts just to tide you over.